In land grid array (LGA) technology, large area rasters or two-dimensional arrays of elastomeric contacts, made of a resilient material, each form an electrical column-shaped interconnection when compressed between an input-output pad on a contact plane surface of a modular structure (e.g., an integrated circuit chip on a carrier or a multi-chip module (MCM)) and a vertically arranged input-output contact location on a surface of a printed circuit board. Each elastomeric contact will provide good electrical conductivity, as long as the column-shaped interconnection remains in compression and in the presence of an opposite direction restoring force that is provided by the compressed elastomeric material. LGA technology has the promise of providing large area, reliable, and steady contacting connections that are spatially close to each other, with those connections, as an array, being readily attached and detached.
As LGA technology is developing, dimensional and pressure control of the array is taking on increasing importance. The fabrication of LGAs is evolving to where the elastomeric contact members are carried on a supporting frame arrangement that provides separation dimension setting members at selected places in the array raster. Compression stop members, known in the art as “downstops,” are positioned at selected locations at the edge of the array, so that as the integrated circuit chip module and the printed circuit board are compressed toward each other, the elastomeric contacts deform until the module material reaches the downstop location. This then establishes a selected value two direction gap, of elastomer contact area and a select initial quantity of an opposing pressure to the compression pressure across each elastomeric contact.
In the technology, many of the specifications of the elements involved are interrelated and involve tradeoff considerations. For a dimensional perspective, elastomeric contacts in the range of less than 0.5 millimeter diameter and less than 30 mils in length are being approached.
The state of the art is generally described in J. Xie et al., An Investigation on the Mechanical Behavior of Elastomer Interconnects, PROCEEDINGS OF THE 1999 INTERNATIONAL SYMPOSIUM ON MICROELECTRONICS, Pgs. 58-63 (hereinafter “Xie”), the disclosure of which is incorporated by reference herein. Xie points out that there are many structural and environmental factors that can influence elastomeric contact quality and illustrates the handling of arrays of interconnects in a thin plastic sheet. LGAs of elastomeric contacts, sometimes called buttons, or collectively as metal polymer interposers, when mounted in a border frame, are available from manufacturers, such as Tyco Electronics Inc. of Attleborough, Mass.
With arrays of elastomeric contacts, however, there is a chance that, during compression, contacts will expand out laterally and/or in some other way distort and come in contact with each other. This can result in shorting. The potential for unwanted contact to occur is increased as device dimensions decrease, requiring contacts to be placed closer together.
Therefore, contact arrays wherein compression is regulated, e.g., during temperature changes, and wherein unwanted interactions between contacts is minimized or eliminated, would be desirable.